1. Field of the Invention
The present invention relates in general to operational control for self-propelled robots such as self-propelled robot cleaners and, more particularly, to a device and method for controlling the tension of a power cord of such a self-propelled robot for releasing the tension applied on the power cord in occurrence of a sudden happening or in rapid self-propelled turning motion of the robot during operation of the robot, thereby preventing possible deviation of the self-propelled robot from its intended running (travel) direction.
2. Description of the Prior Art
There have been proposed devices for controlling the tension of power cords of self-propelled robots, such as self-propelled vacuum cleaners, as disclosed in this inventor's U.S. patent application No. 08/175,536 filed on Dec. 30, 1993). The typical cord tension control device disclosed in the above U.S. patent application is shown in the accompanying drawings, FIGS. 1A and 1B. As shown in these drawings, the cord tension control device includes a plate spring 720 adapted for provision of cord rewind tension for a power cord designated by the numeral 300. Mounted on the casing wall of the control device are first and second optical sensors 210 and 220, each adapted for sensing draw-in and draw-out motions of the power cord 300 and the length of cord extension and retraction. The cord tension control device also includes a motor 500 for keeping a predetermined constant tension of the power cord 300 by tightening or loosening the spring 720. The inner end of the spring 720 is fixed to a shaft 721 driven by motor 500, and the outer end of the spring is fixed to a spool 710 on which the cord 300 is wound.
The above cord tension control device somewhat reliably keeps the predetermined constant tension of the cord 300 in response to variation of distance between the self-propelled robot and a plug socket when running on a flat surface. However, the cord tension control device has a problem that it can not precisely rapidly control a high tension instantaneously applied on the cord 300 in occurrence of a sudden happening or in response to a rapid self-propelled turning motion of the robot during operation of the robot.
When the cord 300 is subjected to such instantaneously increased tension, the wheels of the self-propelled robot may slip, so that there occurs not only abrasion of the wheels but also a deviation of the robot from its intended running direction.